1. Field of the Invention
The present invention relates to a transflective liquid crystal display device for portable electronic devices.
2. Description of the Related Art
In portable electronic devices such as a mobile phone or a portable game device, since duration of battery life time significantly affects its usability, a reflective liquid crystal display device having low power consumption has been employed as a display device. The reflective liquid crystal display device typically comprises a reflector for totally reflecting the external light incident from the front surface thereof or a reflector for reflecting the external light incident from the front surface and for transmitting the backlight from the back surface.
Among these reflectors, the reflector for reflecting the external light incident from the front surface and for transmitting the backlight from the back surface is commonly referred to as a transflective reflector. For example, as the transflective reflector, transflective film made by forming apertures in a certain region of a metal thin film is used (for example, see Japanese Unexamined Patent Application Publication No. 2001-222009). The region in which the apertures are formed is a dot region corresponding to three dots colored Red, Green, and Blue included in a plurality of pixels formed in the liquid crystal display panel.
In a conventional transflective liquid crystal display device in which a transflective reflector is formed on the liquid crystal display panel and an illumination device such as the backlight unit is provided on the back surface of the liquid crystal display panel, the light from the illumination device is transmitted through the aperture in the transflective film toward the surface of the liquid crystal display panel when the illumination device is turned on (in the transmission mode) and the external light is reflected toward the surface of the liquid crystal display panel at the portion (reflection region) other than the aperture in the transflective reflector when the illumination device is turned off (in the reflection mode). Thereby, the liquid crystal display panel can be brightly illuminated by any light source of the illumination device and by the external light.
FIG. 19 is a plan view showing the arrangement of an aperture 132 formed in the dot region 113a of the transflective film corresponding to each of three dots colored Red, Green, and Blue included in each pixel of the liquid crystal display panel equipped in the conventional transflective liquid crystal display device. The aperture ratio of the dot region (the area S1 of the aperture/the area S0 of the dot region) is in the range of 20 to 50%. In addition, in FIG. 19, the reference letters BM indicates a lattice-shaped black matrix formed on the transflective film and dots (not shown) are formed in the inner side of the black matrix BM. The width WBM of the black matrix BM is in the range of about 5 to 25 μm taking into consideration that the lamination leads to the alignment of about a few μm.
For example, the longitudinal length LD of one dot region 113a is 285 μm, and the width WD thereof is 95 μm. At this time, the longitudinal length LH of the aperture 132 is 143 μm, and the width WH thereof is 50 μm. Also, the interval PH of the adjacent apertures 132, 132 of two adjacent dot regions 113a, 113a in a plurality of dot regions arranged in the longitudinal direction is 142 μm.
However, in case that the above-mentioned conventional transflective liquid crystal display device is in the transmission mode when the display mode is in a normally white mode, a band-shaped dark portion G (the portion shown by a hatched line in FIG. 19) that extends in a horizontal direction in the display shown by the range A is generated when turning on six dots (three in the horizontal direction×two in the vertical direction) of the range A surrounded by a dotted line in FIG. 19, which consequently deteriorates the display quality. Also, in case that the above-mentioned conventional transflective liquid crystal display device is in the reflection mode when the display mode is in a normally black mode, if the dots of the lower side (the range D surrounded by a dotted line in FIG. 19) are turned on when turning on three dots (horizontal direction 3×vertical direction 2) in the range C surrounded by a dotted line in FIG. 19, the reflection portion between the range C and the range D appears on the reflection display region, and the display is deviated by a half pixel, which also consequently deteriorates the display quality. Further, even in case that the display mode is in a normally white mode, the band-shaped dark portion is generated in the display or the display is deviated by the half-pixel.